Manual

Use of a rapid arterial blood gas analyzer to estimate blood hemoglobin concentration among critically ill adults
Joel G Ray1,2 , Julia R Post1 and Cindy Hamielec1

1 Division of Critical Care, Department of Medicine, McMaster University, Hamilton, Ontario, Canada

2 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada

author emailcorresponding author email

Critical Care 2002, 6:72-75doi:10.1186/cc1456

Received: 5 October 2001
Accepted: 24 October 2001
Published: 19 November 2001

© 2002 Ray et al., licensee BioMed Central Ltd

Abstract
Objective
To evaluate whether measurement of the hemoglobin (Hb) concentration with a blood gas analyzer approximates that determined by a conventional coulter counter incritically ill adults.

Design
Prospective patient series.

Setting
A 32-bed cardiovascular, neurosurgical, trauma and medical-surgical intensive care unit in a single Canadian center.

Patients
We consecutively recruited 202 critically ill adults, the majority of whom had recent cardiac or vascular surgery, neurosurgery or trauma.

Measurements
The nurse obtained a single arterial bloodsample within a few hours of the patient's admission to the intensive care unit. The Hb concentration was determined from each blood sample in a masked fashion, using both a blood gas analyzer and a conventional laboratory coulter counter.

Main results
A total of 202 consecutive paired analyses were conducted. There was a highly significant correlation between the coulter counter and blood gasanalyzer methods of Hb measurement (r2 = 0.98, 95% confidence interval [CI] = 0.97–0.99; P < 0.0001). Using the method of Bland and Altman, the overall mean difference in Hb concentration between the coulter counter and the blood gas analyzer was -4.3 g/l (95% CI = -11.0 to 2.4). Of the 11 (5.4%) Hb measurements that extended beyond the upper and lower 95% CI, 10 (5.0%) were within ± 3 g/l of theseconfidence limits.

Conclusions
An arterial blood gas analyzer may provide a valid alternative method to the traditional coulter counter for the rapid assessment of Hb concentration among critically ill adults. Since issues related to its safety, quality control, data entry and cost savings have yet to be addressed, however, use of such point of care testing should be viewed as a supplement toconventional laboratory testing.

Keywords:
arterial blood gas; coulter counter; critical care; hemoglobin concentration; intensive care unitIntroduction
The frequent collection of blood specimens in the intensive care unit (ICU) may contribute to iatrogenic blood loss [1,2], compounding the problem of acute anemia that is frequently found among individuals with active hemorrhage, with ableeding diathesis or with hemodilutional anemia [3]. The lag time in the diagnosis of severe acute anemia, due to long laboratory turnaround times, may have important clinical consequence [2,4,5]. The availability of arterial blood gas (ABG) analyzers in most ICUs and hospital laboratories enables rapid analysis of not only traditional blood gas elements, such as pH and pO2, but also Hb concentration.Because little is known about the accuracy of ABG analysis for the determination of Hb concentration, we prospectively evaluated its use in a critical care setting.

Methods
This study was conducted at the Hamilton General Hospital, a 32-bed medical and surgical ICU covering treatment that includes trauma, neurosurgical and cardiovascular sub-specialty care. All consecutive patients admittedto the ICU during the period between 18 June and 16 July 2000 were included. As part of their routine admitting bloodwork, an arterial whole blood specimen was obtained from each patient by his/her ICU nurse, shortly after admission to the ICU. A portion of that specimen was placed directly into a heparinized ABG gas syringe, while the remainder was placed in an EDTA vacuum collection tube. The...